Astrocytes and oligodendrocytes are thought to develop from multi- potential glial precursor cells, termed O2A progenitor cells. The development and differentiation of O2A progenitor cells has been studied extensively in tissue culture systems. Although cells with some of the surface properties of O2A progenitor cells have been identified in developing and adult animals, their developmental pathways and functions are poorly understood. The goals of this proposal are to investigate the development and functions of an unusual class of glial cells that express the NG2 chondroitin-sulfate proteoglycan, a cell surface marker for O2A(neonatal) and O2A(adult) progenitor cells. The role of these cells in the glial reaction to injury will be investigated using 3 models; 1) puncture injury which induces a robust astrogliosis, 2) retrograde neuronal degeneration which follows section of a cranial nerve, and 3) transient demyelination which is a model for the early stages of multiple sclerosis. Immunocytochemical experiments will characterize the changes that occur in adult progenitor cells, microglia, astrocytes and oligodendrocytes following these experimentally induced injuries. Thymidine autoradiography will be used to identify cells stimulated to divide by injury and follow their fate over time. The ability of damaged tissue to support the attachment and growth of neonatal neurons will be investigated using a cyroculture assay system that is amenable to biochemical and immunological manipulations. Additional experiments will identify mitogens for the NG2-positive glia isolated from adult animals and determine whether the expression of these mitogens is increased after injury. These experiments will contribute to an understanding of the biochemical and cellular features of the damaged central nervous system and identify potential cellular targets for therapies designed to encourage axon regrowth and remyelination. A second series of experiment will investigate the role of the environment as a determinant of glial cell fate. Clonally related, undifferentiated glial precursor cells will be injected into different regions of the developing CNS and their subsequent differentiation analyzed using cell type specific marker antibodies. The hypothesis that endogenous glial precursor cells develop along different pathways according to their location will be investigated using a retroviral cell marking technique. These developmental studies will add to our understanding of the mechanisms of cellular determination in the nervous system.